The invention relates to improvements in dispensers for pastes, creams and other viscous or highly viscous materials. More particularly, the invention relates to improvements in dispensers of the type wherein a material-containing cylinder is reciprocable relative to a carrier (such as a tubular housing) and has an outlet for evacuation of material from its interior, and wherein a piston is movably installed in the cylinder so that it can move in a direction to reduce the effective volume of the material-confining chamber of the cylinder.
It is already known to design a dispenser of the above outlined character in such a way that an end wall of the cylinder moves toward the piston when the cylinder is moved with reference to the housing in a direction to expel material from the chamber, and that the piston shares the movement of the cylinder in opposite direction back to a starting position. The piston seals or nearly seals the cylinder at one end of the chamber. The housing carries a depressible actuator which can move the end wall of the cylinder toward the piston to thus ensure expulsion of a desired quantity of viscous material by way of the outlet. The housing further contains a spring which biases the cylinder and its end wall back to a starting position. The spring operates between the housing and a collar of the outlet to pull the cylinder to its starting position. The outlet is a tubular insert, i.e., a separately produced part, which is attached to the major part of the cylinder subsequent to insertion of the spring into the housing.
A drawback of the just described dispenser is that it comprises a large number of separately produced parts. In addition the dispenser is not reliable because the separately produced tubular insert which constitutes the outlet is likely to be separated from the major part of the cylinder. In order to reduce the likelihood of such separation, it is necessary to establish a highly reliable connection between the insert and the major part of the cylinder. Another drawback of the aforedescribed dispenser is that the cylinder is likely to jam, i.e., the spring cannot return the cylinder to its starting position if some of the confined viscous material happens to penetrate between the housing and the cylinder. Moreover, the movement of the cylinder back to its starting position is slow, especially if viscous material is permitted to penetrate between the cylinder and its housing. The spring is likely to lose its resiliency after a certain period of use or on prolonged storage of the dispenser. The bias of the spring cannot be increased at will because a strong or very strong spring would be even more likely to extract or otherwise separate the tubular insert from the major part of the cylinder, i.e., it is not possible to ensure a predictable and reasonably rapid return movement of the cylinder to its starting position by employing a spring which can invariably overcome the resistance of viscous material between the cylinder and the housing. Last but not least, the operator of the dispenser must overcome the bias of the spring whenever the actuator is depressed for the purpose of ensuring that the end wall of the cylinder will cooperate with the piston and expel a desired quantity of material from the chamber.
U.S. Pat. No. 4,479,592 to Rusing et al. discloses a modified dispenser wherein the bottom wall of a tubular housing for the cylinder carries an elongated guide for the piston and the piston carries a spring which cooperates with the cylinder to prevent the piston and the cylinder from moving relative to each other in a direction to enlarge the effective volume of the material confining chamber in the cylinder. An end wall of the cylinder extends from the housing and can be depressed to move toward the piston in order to expel a desired quantity of viscous material from the chamber. A compression spring in the housing serves to return the cylinder to an extended position in which the end wall is ready to be depressed again in order to expel viscous material from the interior of the cylinder by way of an outlet in the end wall. A stop is provided to limit the extent of movement of the cylinder under the action of the spring.
The dispenser of Rusing et al. exhibits the drawback that the compression spring occupies a substantial amount of space in the interior of the housing. This shortens the stroke of the cylinder in a direction to expel viscous material. In addition, the person in charge of expelling viscous material by way of the outlet in the end wall of the cylinder must overcome the resistance of the compression spring. Still further, the likelihood of jamming of the cylinder in the housing is ever present.